Sulfur pelletizing

ABSTRACT

Solid sulfur pellets are prepared from molten sulfur using a gun and pelletizing chamber. Sulfur is ejected from a gun in a form of a thin sheet and dispersed and solidified into solid pellets with a water jet. The pellets and water are separated.

This is a division of application Ser. No. 399,258, filed 9/20/73 nowU.S. Pat. No. 3,887,130.

BACKGROUND OF THE INVENTION

The present invention relates to a method for prilling sulfur. Moreparticularly, this invention relates to a method for preparing hardbeads or prills of elemental sulfur.

Sulfur is one of the essential elements needed for plant life. In manyareas of the world, there is an insufficient amount of sulfur in thesoil to adequately support plant life. Moreover, in alkaline soils,sulfur is not only needed to support plant life, but is also required asa soil supplement. As a soil supplement, sulfur increases the waterintake and aeration of the soil, improves the physical conditions of thesoil, eliminates the harmful alkalinity and sodium problems of the soil,and increases the availability of certain nutrients and elements forplant growth and life.

Elemental sulfur can be added to the soil in many forms such as: thesulfate form, e.g. calcium sulfate; the sulfide form, e.g. ammoniumsulfide or calcium sulfide, elemental sulfur and the like. Elementalsulfur is preferred because it is oxidized in the soil by microorganismsto a form which is the desirable form for plant nutrition and soilimprovement.

Elemental sulfur is available in many forms, such as pellets, flakesulfur, ground sulfur, finely powdered sulfur and the like. Finelypowdered sulfur is rarely used because it is difficult to handle andeasily becomes air born to form dust clouds. Sulfur dust is veryirritating to the lungs of both man and animal and presents an explosivehazard.

Flake sulfur contains a large percentage of water and is easily brokenup during transportation and handling creating dust fines which areeasily air born. Ground sulfur is also difficult to handle and tends topowder upon handling and during transportation. Prilled or pellet sulfuris an improvement over the above forms of sulfur; however, the prilledor pellet sulfur formed by the conventional methods contains a highpercentage of water, is somewhat friable and is easily broken up duringtransport and handling creating dust fines, and is not uniform in size.

The present invention provides a method for producing prilled sulfurwhich has a low percentage of water, is durable and not readily friableand, is of uniform size.

Many attempts have been made in the prior art to produce a prilledsulfur having properties of the prilled sulfur produced by the presentinvention without success. For example, the Perry U.S. Pat. No.1,285,358 discloses a process for the preparation of globules whichcomprises spraying molten sulfur into air wherein small globular bodiesof sulfur are formed. The Bacon et al. U.S. Pat. No. 1,378,084 and theCampbell U.S. Pat. No. 3,334,159 both disclose somewhat similar methodsfor prilling sulfur. These methods consist of allowing molten sulfur todrop through a perforated plate to form droplets or shot like bodies ofsulfur which are immediately immersed in a cool aqueous solution tosolidify the molten sulfur shot. These processes produce sulfur pelletsof non-uniform size, containing a high water content. The Nashner et al.U.S. Pat. No. 3,034,864 and the Landucci et al. U.S. Pat. No. 3,484,201disclose a method for preparing sulfur prills from sulfides. Metalsulfides are oxidized to form molten elemental sulfur globules in anaqueous sulfuric acid slurry. The slurry is cooled to solidify thesulfur globules. These processes yield sulfur pellets of non-uniformsize, contaminated with water and/or other impurities. The Canadian Pat.No. 824,608 (issued Oct. 7, 1969) discloses a method for prilling sulfurby spraying molten sulfur out of a gun. The sulfur spray is cooled withsteam and/or water to solidify the sulfur pellets which fall to theground and are collected. This process has been commercially used andproduced sulfur pellets having fairly good handling characteristics, butthe pellets are not particularly uniform in size. The British Pat. No.763,936, published Dec. 19, 1956 discloses a variant of the Nashner etal. and Landucci et al. process described above. The British processconsists of dispersing impure sulfur in an aqueous sulfuric acid attemperatures exceeding the melting point of sulfur to agglomerate thesulfur into pellets. The molten pellets are separated from the slurryand dispersed in water containing a surfactant for the sulfurimpurities. The water is heated to a temperature in excess of themelting point of sulfur to obtain agglomeration and then is cooled tobelow the melting point of the sulfur to solidify the sulfur globules.The process disclosed in British Pat. No. 1,001,486 is a variant of theabove process. In this process, molten sulfur is dispersed in an aqueousmedium to form molten sulfur globules. The sulfur globules are thencooled to form solid discrete particles of sulfur which are separatedfrom the aqueous medium. In all the above processes wherein the sulfurpellets are formed in an aqueous medium and solidified therein, theresulting pellets contain a fair quantity of water and the otherimpurities contained in the aqueous medium.

SUMMARY OF THE INVENTION

In the present invention, molten sulfur is shot from a sulfur gun as aplurality of discrete streams or jets of molten sulfur. The streams ofmolten sulfur are shattered by a plurality of water jets to formglobules of molten sulfur of substantially uniform size. Alternatively,steam jets can be used to shatter the streams of molten sulfur. Theglobules of molten sulfur are rapidly cooled by a water/steam fog ormist and are thereafter passed through the air to dry them prior totheir collection. The resulting pellets have a hard, glistening surfacewhich is fairly impervious to water.

The equipment which can be employed in the present invention consists ofa sulfur gun and a pelletizing chamber. The gun has a barrel, a head andan interchangeable spray nozzle unit. The pelletizing chamber ispositioned, approximately, perpendicular to the gun. On one side of thepelletizing chamber is located a large aperture through which thestreams of the molten sulfur from the gun are shot into the chamber. Inthe chamber water/steam jets are employed to shatter the streams ofmolten sulfur to form molten sulfur pellets. In addition, a water/steamspray in the chamber is used to cool and solidify the molten sulfurpellets. On the other side of the chamber, there is a second aperturelarger than the first aperture through which the cooled solidifiedsulfur pellets pass and exit into the air. The pellets fall through theair to a recovery area. A substantial proportion of the water from thewater jet and water fog remains in the chamber and falls to the bottomthereof wherein it can be collected, pumped to a holding tank and thenpumped back to the water jets and nozzles of the chamber.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of sulfur pelletizing apparatus which can be usedin the present invention;

FIG. 2 is a cross-sectional view of the sulfur pelletizing apparatuswhich can be used in the present invention taken along line 2--2 of FIG.1;

FIG. 3 is a top-sectional view of the sulfur pelletizing apparatus whichcan be used in the present invention taken along lines 3--3 of FIG. 1;

FIG. 4 is a front-sectional view of the sulfur pelletizing gun which canbe used in the present invention;

FIG. 5 is an enlarged cross-sectional view of the pelletizing gun headtaken along lines 5--5 of FIG. 4 which can be used in the presentinvention;

FIG. 6 is another enlarged cross-sectional view of the head of thepelletizing gun head taken along lines 6--6 of FIG. 4 which can be usedin the present invention; and

FIG. 7 is a perspective view of a sulfur pelletizing plant in which thepresent invention can be used.

DETAILED DESCRIPTION OF THE INVENTION

The sulfur prilling apparatus 8 which can be used in the presentinvention is illustrated in FIG. 1. The apparatus 8 consists of a sulfurgun 10 and a prilling chamber 12. The gun 10 has a barrel 14, a head 15attached to one end of the barrel, and a support base 16 which issecured to the barrel near its other end. Within the barrel 14 there isa chamber 14a for molten sulfur. The gun 10 is balanced about thesupport base 16 by a counter-weight 17 which is attached to the end ofthe barrel 14 opposite the head 15. The base 16 has an inlet 16a formolten sulfur which communicates with the chamber 14a. An inlet 18a islocated at this end of the barrel and is in communication with a steamconduit 19 which is in communication with a central heating chamber 38in the head 15 as is further described in FIG. 3. A condensate streamoutlet 18b is located on the front of head 15. The conduit 19 ispositioned coaxially within the barrel 14. The outer wall of conduit 19and the inner wall of the barrel 14 define the boundaries of the chamber14a. The head 15 and the barrel 14 are connected by sleeve 20. A steaminlet 21a is connected to the top of the head 15 and a steam/condensateoutlet 21b is connected to the bottom of the head 15. The inlet 21a andoutlet 21b are connected to a heating chamber 41 in head 15 as describedbelow and shown in FIG. 3.

The prilling chamber 12 has a vertically oriented cylindrical wall 23,the bottom portion which is connected to a conical base 24.

A water outlet 25 is connected to the apex of the conical base 24. Thecylindrical wall 23 has a circular opening 27 on the left side and asquare opening 28 on the right side opposite opening 27 and coaxialtherewith. Two conduit rings, 30 and 31 are located in chamber 12between openings 27 and 28 and coaxial therewith. The gun 10 isapproximately coaxial with the two openings 27 and 28.

The head 15, the openings 27 and 28, and the ring 31 are illustrated inFIG. 2. As can be seen in FIG. 2, the opening 27 is slightly larger thanthe diameter of the head 15. Similarly, the width and the height ofopening 28 is slightly larger than the diameter of the conduit ring 31.A series of water nozzles 33 are circumferentially positioned around theinner side of the ring 31 and extend radially inward therefrom. Nozzles33 are water fog or spray nozzles. A series of water jet nozzles 34 (seeFIG. 3) are circumferentially positioned around the inner side of thering 30 and extend radially inward therefrom in a fashion similar tonozzles 33 on the ring 31. On the face of head 15 there is an annularnozzle plate 35 which is secured to the face of head 15 by a pluralityof retaining screws 36. Circumferentially spaced about the annular plate35, approximately equal distance, are a plurality of apertures 37.

In FIG. 3, the relationship between the openings 27 and 28, rings 30 and31 and the gun 10 is clearly shown. Conduit 19 within the barrel 14communicates with a central heating chamber 38 in head 15. Chamber 14acommunicates with a distributing chamber 40 which in turn communicateswith apertures 37 of the plate 35. Inlet 21a and outlet 21b (see FIG. 1)communicate with an outer heating chamber 41 in the head 15. The chamber38 communicates with outlet 18b. Within the chamber 12, there arelocated the conduit rings 30 and 31. The ring 30 has a plurality of jetsfor water and/or steam 34 which are circumferentially spaced within thering 30 and directed radially inward. In a similar fashion, the ring 31has a plurality of spray or mist nozzles 33 which are spacedcircumferentially within the ring and directed radially inward.

Details of the annular nozzle 37 on the face of head 15 are shown inFIG. 4. The face of head 15 has an annular opening of the requireddimensions to receive the annular plate 35; circumferentially aroundthis annular opening, there are located a plurality of support lugs 42which support and brace the plate 35. Each lug has a threaded holeadapted to receive a retaining screw 36. The relationship of the supportlug 42, retaining screws 36 and annular plate 35 is shown in detail inFIG. 5. The relationship between the distribution chamber 40 andapertures 37 in the annular plate 35 is clearly shown in FIG. 6.

A sulfur pelletizing plant 50 in which the present invention can be usedis illustrated in FIG. 7. Molten sulfur is received at the pelletizingplant 50 through line 53 which discharges into a holding tank 54 wherethe molten sulfur is maintained at a controlled temperature forpelletizing. A pump 55 pumps the molten sulfur from tank 54 via line 56and line 57 into the sulfur pelletizing gun 10 via inlet 16a. Steam issupplied from a heating system (not shown) to inlets 18a and 21a of gun10 via steam line 59. Water for the jet and fog ring conduits 31 and 30is pumped from a reservoir tank 60 by a pump 61 through lines 62, 63 and52 into rings 30 and 31. Water sprayed from the rings 30 and 31 iscollected in the bottom of prilling chamber 12 (shown in cut-away) andfed into the holding tank 60 via conduit 25. The discharged steam andcondensate from the gun 10 is discharged through outlets 21b and 18b(shown in FIG. 1) and conduit 65 for recycle to the heating system (notshown).

The operation of pelletizing method is illustrated in FIG. 3. Hotsteam/water is passed into central heating chamber 38 via the conduit19. Similarly, hot steam is passed into the outer heating chamber 41 byway of inlet 21a (shown in FIG. 1). Molten sulfur is pumped into chamber14a via inlet 16a (shown in FIG. 1). The sulfur flows into distributionchamber 40 wherein, under pressure, it is forced out through apertures37 of the annular plate 35 to form a plurality of discrete streams 43 ofmolten sulfur. The sulfur normally is introduced into the gun under apressure of about 50 psig although other pressures are applicable. Aplurality of water jets 44 from water jet nozzles 34 collide with thestreams 43 at approximately a perpendicular angle and disperse thestreams of molten sulfur into globules of molten sulfur 45 having asubstantially uniform size. The water jets normally have a pressure offrom about 75 to about 100 psig, although other pressures can beemployed. The initial momentum of the molten sulfur carries the moltensulfur globules 45 across the width of the prilling chamber 12 whereinthe globules 45 of molten sulfur enter a zone of water spray/fog 46 fromnozzles 33. The water spray/fog 46 cools and solidifies globules 45 intosulfur pellets 47. The momentum of the solid sulfur pellets 47 issufficient to carry the pellets across the remaining distance of chamber12 out through opening 28 into the air where the pellets fall to arecovery area (not shown). Most of the water from water jets 44 and thewater fog or spray 46 remains within the confines of chamber 12 andfalls to the bottom thereof. The slight amount of water that does adhereto the pellets 47 is rapidly evaporated and removed from the pellets bythe air as the hot pellets 47 fall downward towards the recovery bed.Alternatively, the pellets can be projected through a drying chamber(not shown) wherein the pellets are dried with forced aircounter-currently.

The size of the pellets is controlled by the size of apertures 37, bythe velocity of stream 43, and/or by the force of jet 44. Normally, theforce of jet 44 and the velocity of stream 43 will remain fairlyconstant and it is easy to adjust the sulfur pellet size by employingdifferent annular nozzles 35 with different size openings and spacingrelationships.

The sulfur in holding tank 54 is controlled to a temperature between245° and about 265° F. The molten sulfur is then pumped to gun 10 at arelatively constant pressure. The gun is normally positionedhorizontally.

It can be readily seen, that the sulfur prilling apparatus which can beused in the present invention is relatively simple and economical tomaintain and operate. The annular nozzle 35 can be readily changed. Theprilling chamber 12 is large and provides easy access for maintenanceand cleaning.

The momentum of the sulfur streams 43 is generally sufficient to projectthe solidified sulfur pellets 47 for about 60 to about 100 feet from thegun, thus allowing adequate time for air drying of the pellets andproviding that the base and the area around the chamber 12 remain freeof sulfur.

Normally sulfur pellets range from about 0.5mm to about 5mm in diameterand can be readily manufactured by the present method.

What is claimed is:
 1. A process for the production of solid sulfurpellets which comprises the steps of:a. forming a stream of moltensulfur; b. shattering said stream of molten sulfur by streams ofmaterial selected from the group consisting of steam and waterintersecting said stream of molten sulfur at approximately right anglesto form globules of molten sulfur; and c. cooling said globules ofmolten sulfur wherein said globules are solidifed to sulfur pellets. 2.The process according to claim 1 in which the sulfur pellets arerecovered.
 3. The process according to claim 1 in which the sulfurpellets of step c vary in size from about 0.5 mm to about 5 mm.
 4. Theprocess according to claim 1 in which the globules of molten sulfur ofstep c are cooled by a water spray.
 5. The process according to claim 1in which the globules of molten sulfur of step c are cooled by a steamspray.
 6. A process for preparing solid sulfur pellets from moltensulfur which comprises the steps of:a. passing molten sulfur through aplurality of apertures to form a plurality of streams of molten sulfur,said apertures being positioned in a circular fashion so that thestreams of molten sulfur form the general shape of a cylinder; b.shattering the streams of molten sulfur by intersecting said streams ofmolten sulfur with streams of material selected from the groupconsisting of water and steam at approximately right angles to formglobules of molten sulfur; and c. solidifying the globules of moltensulfur to sulfur pellets by cooling said globules with a coolantselected from the group consisting of a steam spray and a water spray.7. The process according to claim 6 which includes the additional stepof passing the sulfur pellets through air to dry said pellets.
 8. Theprocess according to claim 7 in which the dry pellets are recovered. 9.The process according to claim 8 in which the recovered pellets vary insize from about 0.5 mm to about 5 mm.
 10. The process according to claim6 in which the streams of material used to shatter the molten sulfurstreams and the coolant used to cool the molten sulfur globules arerecovered and recycled.
 11. A process for the production of solid sulfurpellets from molten sulfur which comprises the steps of:a. formingstreams of molten sulfur; b. shattering said streams of molten sulfur bystreams of material selected from the group consisting of water andsteam to form globules of molten sulfur, said streams of materialintersecting and shattering said streams of molten sulfur atapproximately right angles; c. cooling said globules of molten sulfurwith a coolant selected from the group consisting of a steam spray and awater spray wherein said globules are solidified to sulfur pellets.